In general, you have to distinguish whether a disc brake on a mountain bike is constantly grinding and makes a noise (often a ringing or regular grinding noise), or whether it only squeals or howls when you apply the brake. If the brake only squeals when braking, the brake pads are usually contaminated. This happens when the pads and/or the brake disc have come into contact with oil or other lubricants. Then they squeak not only annoying but also have a significantly worse braking effect.

Important information in advance: A disc brake is a safety-relevant component. If you tinker with it yourself, you should know what you are doing and, above all, work thoroughly. If you don't have enough experience, it doesn't hurt to visit a bicycle repair shop and get advice from experts.

Quick and easy: Here's what you can do about squealing.

If the brake pads are more contaminated, you need to replace the pads. In the case of small amounts of oil, you can still save the brake pads and clean the disc along with the brake caliper. Here's how:

1. Removing the brake pads: The first thing you need to do is remove the pads from the brake caliper. How to change the brake pads quickly.
2. File off the pads: Then you can file off the dirty surface of the pads (attention: really only the surface) with a file or sandpaper.
3. Clean disc and caliper: After that, you should spray the brake disc and caliper (inside and outside) with brake cleaner and wipe it off with a clean rag.
4. Roughen the brake disc: In addition, you can still roughen the cleaned brake disc slightly with a piece of fine sandpaper. This allows the brake pad and disc to readjust to each other. This is the basis for maximum braking performance.
5. Re-braking: Once the brake pads and wheel have been reinstalled, the brake must be re-braked. To do this, brake the brake really hot several times in a controlled environment so that it can develop its full braking power.

Fastest measure against squeaking disc brakes, which also works on tour: Grinding the surface of the brake pads...

... and the brake disc. However, this works only with little contaminated pads.

Disc brakes squeak in wet conditions

Finally, you can ask yourself how the oil or lubricant got onto the pads or brake disc. The classic: when cleaning with silicone spray or when oiling the chain with a chain spray. Anyone who does this should be more careful in the future. But it can also be that deposits of dust and dirt on the pads cause a lot of noise. This is often the case, especially after the winter. There is nothing you can do to prevent this. Squealing in wet conditions or rain is also more or less normal for disc brakes.